Apparatus for mixing chemicals in fibre suspensions

ABSTRACT

The invention relates to an apparatus for mixing chemicals in fibre suspensions. The apparatus comprises a rotor (8) provided with blades and mounted to rotate in a casing (1) having an inlet (3) and an outlet (5) for the fibre suspension; and an inlet or inlets (6) for chemicals. The rotor (8) comprises a fluidizing and gas separating section (9), a pumping section (10) and a section (12) for mixing chemicals. An inlet (25) for chemicals leads to a space (24) between the pumping section (10) and the mixing section (12). The blades of the mixing section preferably cooperate with the casing wall (17) provided with ribs (18).

TECHNICAL FIELD

The present invention relates to an apparatus for mixing chemicals infibre suspensions, particularly in high consistency cellulose pulps. Thechemicals to be mixed in the pulp can be in a gaseous or liquid form.

Various devices are used in pulp industry for mixing chemicals in pulps.When the consistency is low, i.e. up to approximately 5%, mixing doesnot usually cause problems. At higher consistencies, e.g. 5-15%, mixingis, however, more difficult as the gas content, mostly air content, ofthe pulp increases with the rise of the consistency and only littleliquid remains between the fibres. The air in the pulp interferes withthe reaction of the chemicals and aggravates pumping of the pulp with acentrifugal pump.

BACKGROUND ART

Swedish patent application No. 7909781-2 discloses an apparatus formixing treatment chemicals in suspensions. The apparatus comprises amixing means consisting of a cylindrical portion provided with axialribs, and of a larger discshaped portion provided with radial ribs. Thehousing of the apparatus is provided with corresponding stationary ribs.When the mixing means rotates the pulp flowing through the passagesbetween the mixing means and the housing is fluidized and chemicals areefficiently mixed in the pulp.

U.S. Pat. No. 4,410,337 discloses an apparatus for separating gas from afibre suspension, in which the fibre suspension is caused to rotate by arotor provided with blades and disposed in the inlet channel of theapparatus so as to bring about a core of gas surrounded by fibresuspension, gas being discharged from the core to a separate gas space.

Further, Finnish patent application No. 823279 discloses an apparatusfor mixing chemicals in fibre suspensions. The apparatus comprises arotor provided with external protrusions and disposed in the casing inthe inlet channel of the centrifugal pump in front of an impeller. Thecasing is provided with an opening or openings through which chemicalscan be supplied to the space between the inlet channel and the rotor.

Until now at least two devices provided each with its own drive havebeen required for pumping pulp, removing the harmful gas and mixingchemicals in the pulp.

DISCLOSURE OF THE INVENTION

The primary object of the present invention is to provide an apparatusthe construction of which is simple and by which gas can be removed froma high consistency pulp, chemicals can be mixed in the pulp and the pulpcan be pumped.

The apparatus makes use of the advantages provided by fluidization inpumping of a pulp and in mixing chemicals in a pulp.

An apparatus according to the invention comprises a rotor provided withblades and mounted to rotate in the casing, an inlet and an outlet forthe fibre suspension, and an inlet or inlets for chemicals. It is acharacteristic feature of the apparatus that the rotor comprises afluidizing and gas separating section, a pumping section and a sectionfor mixing chemicals; and that at least one of the inlets for chemicalsleads to the space between the pumping section and the mixing section orto the pumping section after the gas separating section or to the mixingsection.

As removal of gas from the pulp and mixing chemicals in the pulp can becarried out as consecutive steps in the apparatus used for pumping thepulp, considerable savings are gained in investment, operation andmaintenance costs and in the requirement of space when compared to knowndevices.

As chemicals are mixed in the pulp after gas has been removed, alsogaseous and gasifiable chemicals can be mixed in the pulp with thisapparatus. Expensive chemicals are thus not lost in connection with thegas removal. If chemicals are added to the pulp after pumping, e.g.gaseous chemicals do not disturb pumping.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to theaccompanying drawings in which

FIG. 1 is a cross section of an embodiment of the invention,

FIG. 2 is a section on line A--A in FIG. 1, and

FIG. 3 is a section on line B--B in FIG. 1.

BEST MODE OF CARRYING OUT THE INVENTION

In the figures the reference numeral 1 refers to the apparatus casingwhich consists of two parts. The casing comprises a cylindrical inletchannel 2 into which the fibre suspension to be treated is fed throughan inlet 3. The casing is provided with a flange 4 for fixing theapparatus to a vessel or any other source of fibre suspension. Thecasing also comprises another flange having an opening 5 for thedischarge of the treated fibre material from the apparatus, and an inlet6 for chemicals. The casing is equipped with a shaft 7 rotated by amotor, which is not illustrated in the figures, the shaft being sealedand journalled outside the casing in a way known per se and notillustrated in the figures. A rotor 8, which comprises blades 9, 10, 11and 12 differing from each other in both structural configuration andfunction, and discs 13 and 14 between the blades 10 and 11, and 11 and12 respectively, is fixed to the shaft. Rotor blades 9 in the inletchannel which constitute the fluidizing and gas separating section aresubstantially axial. When the rotor rotates, centrifugal force separatesgas from the fibre suspension and an annular core of gas surrounded by amixture of gas and liquid is created in the inlet channel. The innerrotor blades 10 constituting the pumping section of the rotor extend toa longer radial distance (r₁) from the axis than blades 9, whichincreases the pressure on the fibre suspension by centrifugal force.

Disc 13 comprises an opening or openings 15 through which the gasseparated in the rotor section 0 can be discharged. The function of theblades 11 behind the disc is to separate the fibre material transportedwith the gas through openings 15, in order to minimize the amount offibres in the gas discharged from the apparatus through channel 16.

The rotor blades 12 which constitute the chemical mixing section and arefixed to blades 11 behind the annular disc 14 are substantially radial.To intensify mixing, ribs 18 are disposed in a wall 17 of the casingclose to the range of blades 12 which results in efficient mixing of thefibre suspension in zone 27 between the disc and the casing wall whenthe rotor rotates. Disc 14 is located between an outer surface 20 of adisc 19 disposed inside the casing around the shaft and a sealingsurface 21 provided in the casing in such a way that a partition wall isformed dividing the casing in two chambers 22 and 23 which communicatewith each other through a channel 24. The pumping section of the rotoris loacated in chamber 22 and the mixing section in chamber 23. For thesupply of chemicals between the pumping section and the mixing section,at least one inlet 25, with its feed opening 6, leading to the channel24, is provided in the casing.

The fibres suspension, from which gas has been removed in the gasseparation zone 26 formed by the inlet channel and the rotor blades 9,flows through the pumping zone formed in the chamber 22 by the rotorblades 10 and the casing wall and is after that guided through thechannel 24, in which chemicals are added to it, to the mixing zone 27formed in the chamber 23 by the casing wall 17, which is provided withribs, and the rotor blades 12, in which zone chemicals are evenly mixedin it after which the suspension is discharged through the opening 5.

The gaps between the rotor disc 14 and the sealing surfaces 20 and 21are located so that the direction of the leakage flow is from thepumping zone to the mixing zone which prevents the chemicals from comingout through the gas discharge or the sealing box of the pump.

The invention is not limited to the embodiment presented here as anexample, only, but it can be modified and applied in various ways withinthe scope of protection defined by the patent claims. E.g. the chemicalsupply opening 6 and the channel 24 connecting the chambers 22 and 23can be located beside the discharge opening for the fibre suspensionwhereby the chemicals and the fibre suspension must flow in theinfluence range of the rotor blades 12 almost a whole cycle before theyare discharged from the pump. The apparatus can be provided with severalinlets at an angular distance from each other through which variouschemicals can be introduced into the apparatus. Ungasifiable chemicalscan be added to the apparatus also in the inlet channel 2. The form anddimensions of the blades can differ considerably from the onesillustrated in the drawings.

We claim:
 1. An apparatus for mixing chemicals in a fiber suspension,the apparatus comprising a casing having a first inlet channel at oneend thereof for receiving the fiber suspension; a second inlet forintroducing chemicals to be mixed with the fiber suspension, a firstoutlet for discharging fiber suspension treated with the chemicals, anda second outlet for discharging gas separated from said fibersuspension; a rotor mounted for rotation within the casing, said rotorcomprising a first blade configuration in a fluidizing and gasseparation section located in the first inlet channel of said casing, asecond blade configuration in a pumping section of said casing,downstream of said first blade configuration, and a third bladeconfiguration in a chemical mixing section of said casing; said secondinlet located downstream of said second blade configuration to introducethe chemicals in a channel provided in the casing connecting the pumpingsection and the mixing section.
 2. An apparatus as recited in claim 1wherein said casing includes a wall at least partially forming saidmixing section, said wall being provided with ribs, said third bladeconfiguration cooperating with said ribs to intensify the mixing of thechemicals with the fiber suspension.
 3. An apparatus as recited in claim1 wherein said rotor is mounted for rotation on a longitudinal shaft,said first blade configuration extending substantially axially relativeto said shaft, said second and third blade configurations extendingsubstantially radially relative to said shaft.
 4. An apparatus asrecited in claim 1 wherein said casing is divided into two chambers, thepumping section being located in one chamber, and the mixing sectionlocated in the other chamber, said chambers being interconnected by saidchannel.
 5. An apparatus as defined in claim 1 wherein said rotorincludes a fourth blade configuration located between said second andthird blade configurations.
 6. An apparatus for mixing chemicals in afiber suspension, the apparatus comprising a casing having a first inletchannel at one end thereof for receiving the fiber suspension; a secondinlet for introducing chemicals to be mixed with the fiber suspension, afirst outlet for discharging fiber suspension treated with thechemicals, and a second outlet for discharging gas separated from saidfiber suspension; a rotor mounted for rotation within the casing, saidrotor comprising a first blade configuration in a fluidizing and gasseparation section of said casing, a second blade configuration in apumping section of said casing, a third blade configuration in achemical mixing section of said casing, and a fourth blade configurationlocated between said second and third blade configurations, wherein saidsecond inlet is located to introduce the chemicals in a channel providedin the casing connecting the pumping section and the mixing section, andwherein a first rotor disc is located between said second and fourthblade configurations, said disc provided with openings through which gasseparated in the fluidizing and gas separation section of the casingpasses to said second outlet.
 7. An apparatus as defined in claim 6wherein a second rotor disc is located between said fourth and thirdblade configurations, and a third rotor disc is mounted on said shaftand located radially inwardly of said second rotor disc, wherein saidsecond and third rotor discs comprise a partition wall which divides thecasing into two chambers interconnected by said channel, and whereinsaid pumping section is in one of said chambers, and said mixing sectionis in another of said chambers.